Kernal if defined by someone having two or more chins.The fat rolls under the persons chin and the head expression accociated with it give that person a kernal head.
Also a derivative of KFC founder Colonel Sanders head with it being the foundation to this head expression.
A person with no neck can also be described as having a kernal head.

Look at that fat *(kents) Kernal head.
Man,he's so fat he's got a kernal head.
Dont eat so much otherwise you'll get fat a cop a kernal head.
Look at that fat arsed no necked kernal head.